Get --ftrace working on aarch64

This change implements a new approach to function call logging, that's
based on the GCC flag: -fpatchable-function-entry. Read the commentary
in build/config.mk to learn how it works.

third_party/make/make.mk

@@ -162,15 +162,15 @@ o/$(MODE)/third_party/make/make.com:			\
 o/$(MODE)/third_party/make/strcache.o			\
 o/$(MODE)/third_party/make/expand.o			\
 o/$(MODE)/third_party/make/read.o: private		\
-		OVERRIDE_CFLAGS +=			\
+		CFLAGS +=				\
 			-O2
 
 o/$(MODE)/third_party/make/hash.o: private		\
-		OVERRIDE_CFLAGS +=			\
+		CFLAGS +=				\
 			-O3
 
 $(THIRD_PARTY_MAKE_OBJS): private			\
-		OVERRIDE_CFLAGS +=			\
+		CFLAGS +=				\
 			-DNO_ARCHIVES			\
 			-DHAVE_CONFIG_H			\
 			-DSTACK_FRAME_UNLIMITED		\